Method for Collapsing Microbubbles

ABSTRACT

A method for collapsing a microbubble characterized in that it comprises applying stimulation to the microbubble in the step of the gradual decrease of the its size, in a course wherein the microbubble floating in a solution decreases in its size due to the natural dissolution of a gas contained in the microbubble and disappears after a while, to thereby enhance the speed of the its size decrease and cause the microbubble to disappear.

TECHNICAL FIELD

The present invention relates to a method of collapsing microbubble(microbubbles) that is useful in all technical fields, particularly inthe technical field of water processing.

BACKGROUND ART

Bubbles having a diameter of 50 μm or less (microbubbles) are known tohave properties different form those of normal bubbles, but theproperties of the microbubbles are yet to be understood. For thatreason, various microbubble generators under development recently onlygenerate microbubble of a gas in aqueous solution, and there is almostno invention that makes the most of the potential properties ofmicrobubbles. An example of the traditional technology usingmicrobubbles is the method described in JP-A-2002-143885 of acceleratingthe biological activity, metabolism, and consequently growth oforganisms. However, although the invention has significant advantageousin the field of cultivation of fish and shellfish, it does not discloseor suggest anything about collapsing microbubbles.

An example of the technology using the collapsing phenomenon of bubblesis a method of irradiating ultrasonic wave on bubbles. However, themethod is extremely lower in efficiency because the bubbles forcollapsing are generated by cavitational action of the ultrasonic waveitself, and has a problem of difficulty in commercialization because ofits restricted functions. Most of the cavitation bubbles generated thencontain steam therein and the bubbles are present only for an extremelylimited period of microseconds, and thus, the method had a problem thatit was not possible to use the effects of the gas present in bubbles andthe electric charge formed at the gas-liquid interface collapsingbubbles.

SUMMARY OF THE INVENTION

An object of the present invention, which was made in view of thecircumstances described above, is to provide a method for collapsingmicrobubbles, physical and chemical actions obtained by collapsingmicrobubbles, a method for collapsing the microbubbles by discharge, amethod for collapsing the microbubbles by ultrasonic wave, a method forcollapsing the microbubbles by swirling current, a method for collapsingthe microbubbles by using positive or negative pressure, and a methodfor collapsing the microbubbles by using the catalytic reaction of anoxidizer, as well as a method of decomposing microbes, viruses and thelike, which were considered to be impossible by traditional technology.

The object of the present invention is accomplished by a method forcollapsing microbubbles, characterized in that, in the step of themicrobubbles having a diameter of 50 μm or less floated in a solutiondecreasing gradually by natural dissolution of the gas contained in themicrobubbles and disappearing finally, the microbubbles are disappearedby accelerating the speed of the microbubble size decrease by applying astimulation to the microbubbles.

The object of the present invention is also accomplished moreeffectively by forming an ultrahigh-pressure ultrahigh-temperatureregion inside in an adiabatic compression-like change of themicrobubbles caused by decrease of the microbubbles size; the electriccharge density at the interface of the microbubbles increases rapidlyand a great amount of free radical species are released from thegas-liquid interface; free radical species such as active oxygen speciesfor decomposition of the substances present inside the microbubbles orin the area surrounding the microbubbles are generated by collapsing themicrobubbles; the method gives rise to a compositional change of thechemical substances dissolved or floated in the solution; or the methodsterilizes microorganisms such as microbes, viruses, and others presentin the solution.

Further, the object of the present invention is also accomplished moreeffectively by applying the stimulation is electric discharge in acontainer containing a microbubble-containing solution generated byusing a discharger; the stimulation is ultrasonic wave irradiated into acontainer containing a microbubble-containing solution by anultrasonicator; or the ultrasonicator is connected to the containerbetween a microbubble-containing solution outlet port of a microbubblegenerator connected to container and an intake of the microbubblegenerator and the stimulation is given by continuous irradiation ofultrasonic wave into the container by the ultrasonicator.

When a circulation pipe is connected to a container containing amicrobubble-containing solution, the object of the present invention isalso accomplished more effectively by applying the stimulation iscompression, expansion and swirling current generated by circulatingpart of the microbubble-containing solution in the container by thecirculation pump and making the solution path through an orifice orporous plate having a single or multiple holes installed in thecirculation pipe; the circulation pump gives a positive pressure of 0.1MPa or more to the discharge side; the circulation pump gives a negativepressure lower than the environmental pressure to the intake side; orwhen a circulation pipe is connected to the container containing amicrobubble-containing solution, the stimulation is compression,expansion and swirling current generated by feeding themicrobubble-containing solution in the container into the circulationpipe and making the solution path through an orifice or porous platehaving a single or multiple holes installed in the circulation pipe.

The object of the present invention is achieved more effectively byapplying the the stimulation is forcibly internal circulation, in thepipe for feeding the microbubble-containing solution generated by amicrobubble generator to a container, of making themicrobubble-containing solution discharged from the microbubblegenerator pass through a punching plate installed in the pipe, taken inpart of the microbubble-containing solution from an intake installedbetween the punching plate and the container and feeding it into a pump,feeding the microbubble-containing solution into the pump, dischargingit form an outlet port installed between the microbubble generator andthe punching plate, and making it pass through the punching plate onceagain; or the pump gives a positive pressure of 0.1 MPa or more to thedischarge side; the pump gives a negative pressure lower than theenvironmental pressure in the upstream pipe; the stimulation is acatalytic reaction generated by allowing an oxidant to react in thepresence of a catalyst; the catalyst is copper and the oxidizer is ozoneor hydrogen peroxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the results of measuring the zeta potentialof microbubbles in distilled water.

FIG. 2 is a diagram showing the electrification mechanism ofmicrobubbles in water.

FIG. 3 is a graph showing the relationship between the time period untilmicrobubbles decrease of the microbubble size and disappear and thebubble diameter of the microbubbles.

FIG. 4 is a graph showing the increase in zeta potential associated withdecrease of microbubbles size.

FIG. 5 is a side view of an apparatus for collapsing the microbubbles byusing a discharger.

FIG. 6 is a side view of an apparatus for collapsing the microbubbles byusing an ultrasonicator.

FIG. 7 is a side view of an apparatus for collapsing the microbubbles byusing swirling current.

FIG. 8 is a side view of an apparatus for collapsing the microbubbles byusing positive or negative pressure.

FIG. 9 is a partial side view of the apparatus for collapsing themicrobubbles by using positive or negative pressure.

FIG. 10 is a side view of an apparatus for collapsing the microbubblesin the reaction of an oxidizer in the presence of a catalyst.

FIG. 11 is an ESR spectrum of the free radicals generated duringcollapsing the microbubbles.

EXPLANATION OF NUMERALS

1 Container

2 Discharger

21 Anode

22 Cathode

3 Microbubble generator

31 Intake

32 Microbubble-containing solution outlet

4 Ultrasonicator

5 Circulation pump

6 Orifice (porous plate)

7 Oxidizer-supplying unit

8 Catalyst

9 Pump

10 Punching plate

11 Intake

12 Outlet

BEST MODE OF CARRYING OUT THE INVENTION

As shown in FIG. 1, as a physical property of microbubbles, microbubblesin distilled water have an electric potential of approximately −30 to−50 mV independently of the diameter of bubbles. Thus, for example inwater, as shown in FIG. 2, a microbubble has a structure in which thebubble surface is surrounded by negative ions such as of OH⁻, which inturn are surrounded additionally by cations such as of H⁺ (H₃O⁺).

In addition, a microbubble has a greater specific surface and a higherinternal pressure than a normal bubble, because the surface tension actsmore effectively. It is generally accepted academically that theinternal pressure of a microbubble reaches as high as thousands ofatmospheric pressures when it disappears.

Microbubbles are known to be normally lower rate of climb than normalbubbles and superior in gas dissolving capacity (natural dissolution).Thus, normal bubbles, when generated in water, rising toward the liquidsurface direction and burst at the liquid surface, while microbubblesrising more slowly than normal bubbles and have a superior dissolvingcapacity, thus resulting in gradual decrease in the bubble diameter andfinally disappearance of the bubbles. FIG. 3 shows the results ofmeasuring the time until the microbubble decreases of its size andfinally disappears. The microbubble having a smaller bubble diametershows a shorter time of decrease of microbubble size and disappearanceof the microbubble by natural dissolution. The maximum driving force fordissolving the gas in microbubbles is the self-compression effect bysurface tension. The pressure buildup inside the microbubble withrespect to environmental pressure can be estimated by theYoung-Laplace's Formula.ΔP=4σ/D   (Formula 1)

In the Formula, ΔP represents the degree of pressure buildup; σ, surfacetension, and D, bubble diameter. In distilled water at room temperature,the pressure buildup is approximately 0.3 atmospheric pressure in amicrobubble having a diameter of 10 μm and approximately 3 atmosphericpressures in the bubble having a diameter of 1 μm. The gas in aself-compressed bubble, which behaves in water according to the Henry'slaw in gas phase, dissolves efficiently in ambient water.

On the other hand, the speed of the microbubble size decrease by naturaldissolution rises by application of a physical stimulation such asdischarge, ultrasonic wave, or swirling current to the microbubble, andthus, the microbubble is adiabatic compression and disappears(collapsing). Adiabatic compression of the microbubble then gives riseto an extreme reaction field at ultrahigh temperature and ultrahighpressure when the microbubble disappears.

As described above, an bubble present in water is charged negatively,but there are saturated electric charges formed at the gas-liquidinterface according to environmental conditions such as pH, which can beobserved by the zeta potential of the microbubble. The electric chargesnot due to electrolytic ions and others in water, but are based on thestructural factor of water itself. That is, the electric charges aregenerated by interfacial adsorption of OH⁻ and H⁺ ions, based on thedifference between the hydrogen-bonded network structure at thegas-liquid interface and the structure of bulk. The structure formedalso has an action to suppress thermal molecular movement, and thus, ittakes time of about several seconds to go back to the equilibriumcondition after the electric charge density fluctuates

Decrease of the bubble size by natural dissolution of the microbubble isaccompanied with decrease in the surface area of gas-liquid interface.The surface area of the gas-liquid interface decreases more rapidly asthe bubble becomes smaller, as shown in FIG. 3. When the speed of thedecrease in the surface area of gas-liquid interface is lower, theelectric charge density at the gas-liquid interface remains in thecondition almost in equilibrium. However, as shown in FIG. 4, when thebubble diameter decreases to 10 μm or less, dissipation of electriccharge cannot catch up the speed of the size decrease, which is observedas an increase in zeta potential associated with deviation fromequilibrium. However, the decrease in the surface area of gas-liquidinterface by natural dissolution is not so rapid, and the value ofelectric charge density remains up to several times larger than that inequilibrium, even at the point immediately before disappearance.

In contrast, during the collapsing microbubbles according to the presentinvention, the speed of the decrease in the surface area of gas-liquidinterface is very high, and the electric charge remains as it is withoutdissipation and deviates from equilibrium, resulting in generation of aregion extremely higher in electric charge density. When the bubblehaving a diameter of 20 μm decreases into the microbubble of 0.5 μm orless by collapsing, the electric charge density rises to a value as highas 1,000 times larger than that in equilibrium.

The extremely high-density electric charge formed by collapsing is in anon-equilibrium condition and extremely instable, and the system returnsback to a stable state in a phenomenon different from simpledissipation. Thus, an extremely large potential gradient is formedbetween the bubble interface and its surrounding area in the collapsingprocess, and the equilibrium of the electric charge condition isreestablished by electron transfer, for example, by discharge.

It means generation of an extremely high-density energy field, and whenthe collapsing is performed in water, it is accompanied with generationof free radical species by decomposition of ambient water molecules. Inaddition, because the electric charge carriers are OH⁻ and H⁺, freeradical species such as .OH and .H are formed by neutralization ofelectric charges by discharge.

The free radical species, which are very highly reactive, react withvarious compounds dissolved or suspended in solution, changingcomposition or decomposing the compounds in solution. Because an extremereaction field at ultrahigh temperature and ultrahigh pressure is formedduring collapsing, it becomes possible to sterilize microorganisms suchas microbes and viruses and decompose aromatic compounds such as phenol,although it was hitherto regarded as impossible. Examples of thesubstances decomposed by collapsing include almost all organiccompounds, inorganic compounds such as FeSO₄, CuNO₃, AgNO₃, and MnO₂;dioxins, PCBs, chlorofluorocarbons, microbes, viruses, and the like.

Hereinafter, the method for collapsing the microbubbles will bedescribed.

FIG. 5 is a side view illustrating an apparatus for collapsing themicrobubbles by discharge. The microbubble generator 3 takes in thesolution in a container 1 though an intake 31; a gas is injected intothe microbubble generator 3 through an injection port (not shown in theFigure) for injecting a gas for generating microbubble and mixed withthe solution taken in through the intake 31; and the microbubblesgenerated in the microbubble generator 3 are fed back into the container1 through a microbubble-containing solution outlet 32. In this way,microbubbles are generated in the container 1. An anode 21 and a cathode22 are placed in the container 1, and the anode 21 and the cathode 22are connected to a discharger 2.

First, microbubbles are generated in the container 1 containing asolution by using the microbubble generator 3. The solution in thecontainer 1 used for generation of microbubbles is preferably water(distilled water, tap water, or the like), seawater, or the like; but anorganic solvent such as oil, alcohol, acetone, toluene, or petroleum oilmay also be used. In the present specification, water is used as thesolution for convenience in description, but the present invention isnot limited thereto.

The solution is discharged in the container 1 by using the discharger 2.A saturation bubble concentration of microbubbles in the container 1 ispreferably 50% or more, for more effective collapsing during theunderwater discharge. In addition, the voltage of the underwaterdischarge is preferably 2,000 to 3,000 V. The stimulation of underwaterdischarge raises the speed of microbubble size decrease by naturaldissolution of the microbubbles in water and results in collapsing(disappearance) the bubbles. Extreme reaction fields are formed and freeradicals such as .OH and .H are formed by decomposition of water,simultaneously with disappearance of microbubbles, and the substancesand others present in water are decomposed.

The gas used for generation of microbubbles in the microbubble generator3 is not particularly limited, and may be; or alternatively, themicrobubbles may be generated with ozone or oxygen. Microbubblesgenerated with oxygen or ozone higher in oxidative potential results ingeneration of a greater number of free radical species duringcollapsing, and give an action to decompose hazardous substances andothers superior both in the quantitative and qualitative points as wellas a sterilizing action. Alternatively, the microbubbles may begenerated after oxygen or ozone is previously contained in the solutionin the container.

Hereinafter, a method for collapsing the microbubbles by ultrasonicationwill be described. Description on the devices the same as thosedescribed in the method for collapsing the microbubbles by dischargewill be omitted.

FIG. 6 is a side view illustrating an apparatus for collapsing themicrobubbles by ultrasonic wave. A microbubble generator 3 takes in thesolution in a container 1 though an intake 31; a gas injected into themicrobubble generator 3 through an injection port (not shown in theFigure) for injecting a gas for generating microbubble and mixed withthe solution taken in through the intake 31; and the microbubblesgenerated in the microbubble generator 3 are fed back into the container1 through a microbubble-containing solution outlet 32. In this way,microbubbles are generated in the container 1. An ultrasonicator 4 isinstalled on the container 1. The installation site of theultrasonicator 4 is not particularly limited, but preferably between theintake 31 and the microbubble-containing solution outlet 32, for moreefficient collapsing the microbubbles.

Microbubbles are generated in the container 1 containing water by usingthe microbubble generator 3.

Then, ultrasonic wave is irradiated on the microbubble-containing waterin the container 1 by using the ultrasonicator 4. During collapsing themicrobubbles by ultrasonic wave irradiation, the saturation bubbleconcentration of microbubbles in the container 1 is preferably 50%. ormore, for more effective collapsing the microbubbles. Ultrasonic waveirradiation at a saturation bubble concentration of 50% or more leads tomore efficient collapsing. The irradiation frequency of the ultrasonicwave is preferably 20 kHz to 1 MHz; and the exposure time of ultrasonicwave is preferably 30 seconds or less, but the irradiation may becontinued for an extended period of time.

In the conventional methods of destructing hazardous substances andothers by ultrasonic wave, which were simple irradiation of ultrasonicwave on normal water, lower in the efficiency of generating freeradicals by collapsing, and thus had an insufficient action, it was notpossible to decompose aromatic compounds such as phenol; but it becamepossible to destruct microbes,viruses, and aromatic compounds such asphenol, which were not possible hitherto, by collapsing the microbubblesby irradiating ultrasonic wave on the microbubbles as in the presentinvention.

Hereinafter, a method for collapsing the microbubbles by swirlingcurrent will be described. Description on the devices the same as thosein the method for collapsing the microbubbles by discharge pressure andthe method for collapsing the microbubbles by ultrasonication will beomitted.

FIG. 7 is a side view illustrating an apparatus for collapsing themicrobubbles by swirling current. A microbubble generator 3 takes in thesolution in a container 1 though an intake 31; a gas injected into themicrobubble generator 3 through an injection port (not shown in theFigure) for injecting a gas for generating microbubble and mixed withthe solution taken in through the intake 31; and the microbubblesgenerated in the microbubble generator 3 are fed back into the container1 through a microbubble-containing solution outlet 32. In this way,microbubbles are generated in the container 1. A circulation pump 5 isconnected to the container 1 for partial circulation of themicrobubble-containing solution in the container 1, and an orificehaving multiple holes (porous plate) 6 is placed in the pipe(circulation pipe) which is connected to the circulation pump 5 at oneend and to the container 1 at the other end. Part of themicrobubble-containing solution poured out of the circulation pipe isre-circulated by the circulation pump and an swirling current is formedduring passage through the orifice (porous plate) 6.

First, microbubbles are generated in the container 1 containing water byusing the microbubble generator 3.

The microbubble-containing water is then fed into the circulation pump 5for partial circulation. The microbubble-containing water is further fedby the circulation pump 5 to the orifice (porous plate) 6, and answirling current is formed in the pipe downstream thereof. Themicrobubbles are crushed by expansion or compression of the microbubblesduring passage and by the electric swirling current generated by theswirl of electrically charged microbubbles due to the swirling currentgenerated in the pipe. The positions of the circulation pump 5 and theorifice (porous plate) 6 on the channel may be altered.

Although only one orifice (porous plate) 6 is shown in FIG. 7, multipleorifices maybe installed, and the circulation pump 5 may be eliminatedas needed. Alternatively, the orifice 6 may be replaced with a punchingplate. When a circulation pump 5 is installed, the pressure (positivepressure) of compressing the solution toward the orifice (porous plate)6 is preferably 0.1 MPa or more. A positive pressure of less than 0.1MPa may lead to insufficient eddy current generation. In addition, thepump 5 gives a negative pressure lower than the environmental pressurein the upstream pipe.

FIG. 8 is a side view illustrating a method for collapsing by usingpositive or negative pressure; and FIG. 9 is a partially magnifieddrawing of the area of a punching plate 10 and a pump 9 (the arrow inFIG. 9 indicates the direction of the flow of microbubble-containingsolution). Description on the devices the same as those described abovewill be omitted.

As shown in FIG. 8, it is an apparatus for collapsing of microbubbles bydraining the microbubble-containing water discharged from a microbubblegenerator 3 through a punching plate 10. The punching plate 10 is placedbetween two microbubble-containing solution outlets 32 (between thecontainer 1 and the microbubble generator 3). An intake 11 forcompressing the microbubble-containing solution to a pump 9 is formedbetween the punching plate 10 and the container 1 in themicrobubble-containing solution outlet 32. Part of themicrobubble-containing solution taken in into the intake 11 is fed tothe pump 9 and then further forward by the pressure of the pump 9. Themicrobubble-containing solution is fed by the pump 9 via an outlet port12 formed between the microbubble generator 3 and the punching plate 10into the microbubble-containing solution outlet 32, and passes throughthe punching plate 10 once again. Thus, it is possible to crush themicrobubbles by performing internal circulation forcibly by the pump 9and increasing the swirling current drastically during passage throughthe punching plate 10. The positive pressure of the pump 9 is preferablyadjusted to 0.1 MPa or more for forcibly internal circulation of themicrobubble-containing solution in the microbubble-containing solutionoutlet 32. A positive pressure of pump 9 of less than 0.1 MPa results ininefficient internal circulation. The pump 9 also give a negativepressure lower than the environmental pressure in the intake side(intake 11). The positive pressure is a pressure higher than theenvironmental pressure, i.e., a pressure of the pump 9 feeding thesolution, while the negative pressure is a pressure lower than theenvironmental pressure, i.e., a pressure generated when the pump 9 takesin the solution.

Multiple punching plates 10 may be installed according to application,and multiple pumps 9 may be installed as needed in the method forcollapsing the microbubbles shown in FIGS. 8 and 9. In addition, forexample, a check valve may be installed in the microbubble-containingsolution outlet 32 as needed.

Hereinafter, a method for collapsing the microbubbles by using thecatalytic action of an oxidizer during its reaction. Description on thedevices the same as those described above will be omitted.

FIG. 10 is a side view illustrating an apparatus for collapsing themicrobubbles by using the catalytic action of an oxidizer during itsreaction. A microbubble generator 3 takes in the solution in a container1 though an intake 31; a gas injected into the microbubble generator 3through an injection port (not shown in the Figure) for injecting a gasfor generating microbubble and mixed with the solution taken in throughthe intake 31; and the microbubbles generated in the microbubblegenerator 3 are fed back into the container 1 through amicrobubble-containing solution outlet 32. In this way, microbubbles aregenerated in the container 1. An oxidizer-supplying unit 7 is connectedto the container 1, and an oxidizer is supplied therefrom into thecontainer 1.

Microbubbles are generated in the container 1 containing water by usingthe microbubble generator 3.

Then, a catalyst is added to the container 1. Favorable examples of thecatalysts include various catalysts known in the art, including metalcatalysts such as copper, palladium, iron, vanadium, tin, titanium,zirconium, platinum, manganese, cobalt, nickel, rubidium, rhodium, andzinc; these catalysts may be used alone or in combination of two ormore; and copper is more preferable. The microbubbles may be generatedafter addition of the catalyst into the container 1.

An oxidizer is supplied from the oxidizer-supplying unit 7. The oxidizeris not particularly limited, and any one of various known oxidizers suchas ozone, hydrogen peroxide, sodium hypochlorite, manganese dioxide,sulfuric acid, nitric acid, potassium permanganate, copper chloride, andsilver oxide may be used favorably; these oxidizers may be used alone orin combination of two or more; and in particular, ozone and hydrogenperoxide are more preferable.

Supply of an oxidizer into the container 1 results in generation of veryhigh oxidative radicals in the reaction between the oxidizer and thecatalyst. The radicals accelerate collapsing the microbubbles by theircollision to the microbubbles. Although it is possible to decomposehazardous substances contained in water in the reaction between theoxidizer and the catalyst, it became possible to decompose hazardoussubstances more efficiently and also to decompose and sterilizemicroorganisms such as microbes and viruses, by the collapsing themicrobubbles by using the catalytic action associated with the reactionbetween the oxidizer and the catalyst.

Hereinafter, the methods for collapsing the microbubbles will bedescribed with reference to Examples, but it should be understood thatthe present invention is not restricted thereby.

EXAMPLES Example 1

10 L of phenol-containing water was placed in the container 1 shown inFIG. 5. Microbubbles are generated in the microbubble generator 3 byusing ozone as the gas for preparation of microbubbles and supplied intothe water in the container 1, to give microbubble-containing water. Themicrobubbles were formed continuously, while the saturation bubbleconcentration of microbubbles in the container is controlled to 1 to 50%or more.

Then, the water was electrically discharged at a voltage of 2,400 V tentimes per 10 minutes by the discharger 2, for collapsing themicrobubbles.

Analysis of the water during collapsing by ESR gave the spectrum shownin FIG. 11, confirming the presence of free radical species therein. TheESR spectrum shown in FIG. 11 is determined, as a spin-trapping agent5,5-dimethyl-1-pyrroline-N-oxide (DMPO) is added to the sample. Theresults demonstrated generation of free radicals.

After the collapsing the microbubbles, phenol had been decomposedcompletely.

Example 2

10 L of phenol-containing water was placed in the container 1 shown inFIG. 6. Microbubbles are generated in the microbubble generator 3 byusing ozone as the gas for preparation of microbubbles and supplied intothe water in the container 1, to give microbubble-containing water.Microbubbles were formed continuously, while the saturation bubbleconcentration of microbubbles in the container was controlled to 1 to50% or more.

Then, the microbubbles are crushed by irradiation of an ultrasonic waveat an irradiation frequency of 200 kHz by the ultrasonicator 4 for 10minutes. ESR spectral analysis of the water during collapsing similar tothat in Example 1 gave an ESR spectrum similar to that shown in FIG. 11.

Phenol had been decomposed completely after the collapsing themicrobubbles.

Example 3

10 L of phenol-containing water was placed in the container 1 shown inFIG. 7. Microbubbles are generated in the microbubble generator 3 byusing ozone as the gas for preparation of microbubbles and supplied intothe water in the container 1, to give microbubble-containing water.Microbubbles were formed continuously, while the saturation bubbleconcentration of microbubbles in the container was controlled to 1 to50% or more.

Then, the microbubble-containing water in the container 1 was circulatedpartially, and part of the microbubble-containing water was introducedinto the circulation pipe connected to the circulation pump 5. Themicrobubble-containing water introduced into the circulation pump 5 wasfed to the orifice (porous plate) 6 at a positive pressure of 0.3 MPa,allowing the microbubbles crushed by the swirling current generatedthere.

ESR spectral analysis of the water during collapsing similar to that inExample 1 gave an ESR spectrum similar to that shown in FIG. 11.

Phenol had been decomposed completely after the collapsing themicrobubbles.

Example 4

10 L of phenol-containing water was placed in the container 1 shown inFIG. 8. Microbubbles are generated in the microbubble generator 3 byusing ozone as the gas for preparation of microbubbles and supplied intothe water in the container 1, to give microbubble-containing water.Microbubbles were formed continuously, while the saturation bubbleconcentration of microbubbles in the container was controlled to 1 to50% or more.

Then, part of the microbubble-containing water discharged from themicrobubble generator 3 and passing out of the punching plate 10 wastaken in through the intake 11 by operation of the pump 9 and fed by thepump 9 to the discharge side, for forcibly internal circulation thereofin the microbubble-containing solution outlet 32. The positive pressureof the pump 9 then was 0.5 MPa. The microbubble-containing water fed bythe pump 9 was made to pass through the punching plate 10 once again viathe outlet port 12. Such an internal circulation raised theswirling-current efficiency drastically and was effective in collapsingthe microbubbles.

ESR spectrum analysis of the water during collapsing similar to that inExample 1 gave an ESR spectrum similar to that shown in FIG. 11.

Phenol had been decomposed completely after the collapsing themicrobubbles.

Example 5

10 L of phenol-containing water was placed in the container 1 shown inFIG. 10. Microbubbles are generated in the microbubble generator 3 byusing ozone as the gas for preparation of microbubbles and supplied intothe water in the container 1, to give microbubble-containing water.Microbubbles were formed continuously, while the saturation bubbleconcentration of microbubbles in the container was controlled to 1 to50% or more.

Then, 5 g of a powdery copper catalyst was placed in the container 1,and an ozone gas was supplied from the oxidizer-supplying unit 7 intothe container 1. The amount of the ozone gas supplied was 1 g. Themicrobubbles were crushed by the catalytic reaction associated with thereaction between the ozone gas and the copper catalyst when the ozonegas was supplied.

ESR spectrum analysis of the water during collapsing similar to that inExample 1 gave an ESR spectrum similar to that shown in FIG. 11.

Phenol had been decomposed completely after the collapsing themicrobubbles.

ADVANTAGEOUS EFFECTS OF THE INVENTION

Collapsing the microbubbles by the method according to the presentinvention lead to increase in the speed of microbubbles size decreasedue to utilization of a stimulation (discharge, ultrasonic wave,swirling current, positive and negative pressure, or the catalyticreaction associated with the reaction of oxidizer, or the like),disappearance of microbubbles and generation of active oxygen speciesand free radical species for decomposition of substances present insidethe microbubbles or in the area surrounding the microbubbles, andcompositional change thereby of the chemical substances dissolved orfloated in water; and thus, it became possible to sterilizemicroorganisms such as microbes, viruses, and others present in solutionand decompose aromatic compounds such as phenol, which was difficult inthe past, and thus, to decompose almost all hazardous substances andothers.

INDUSTRIAL APPLICABILITY

By the collapsing the microbubbles according to the present invention,it became possible to sterilize microorganisms such as microbes,viruses, and others present in solution and decompose aromatic compoundssuch as phenol, which were difficult to decompose in the past, and themethod is applicable in the fields for processing hazardous substancesand the like.

1. A method for collapsing microbubbles, characterized in that, in thestep of microbubbles floated in a solution decreasing gradually bynatural dissolution of the gas contained in the microbubbles anddisappearing finally, the microbubbles are disappeared by acceleratingthe speed of the microbubble size decrease by applying a stimulation tothe microbubbles.
 2. The method according to claim 1, wherein themicrobubbles form an ultrahigh-pressure ultrahigh-temperature regioninside in an adiabatic compression-like change of the microbubblescaused by decrease of the microbubbles size.
 3. The method according toclaim 1, wherein the electric charge density at the interface of saidmicrobubbles increases rapidly.
 4. The method according to claim 1,wherein free radical species such as active oxygen species fordecomposition of the substances present inside the microbubbles or inthe area surrounding the microbubbles are generated by collapsing themicrobubbles.
 5. The method according to claim 1, wherein the methodgives rise to a compositional change of the chemical substancesdissolved or floated in the solution.
 6. The method according to claim1, wherein the method sterilizes microorganisms such as microbes,viruses, and others present in the solution.
 7. The method according toclaim 1, wherein the stimulation is electric discharge in a containercontaining a microbubble-containing solution generated by using adischarger.
 8. The method according to claim 1, wherein the stimulationis ultrasonic wave irradiated into a container containing amicrobubble-containing solution by an ultrasonicator.
 9. The methodaccording to claim 8, wherein the ultrasonicator is connected to thecontainer between a microbubble-containing solution outlet port of amicrobubble generator connected to the container and an intake of themicrobubble generator and the stimulation is given by continuousirradiation of ultrasonic wave into the container by the ultrasonicator.10. The method according to claim 1, wherein, when a circulation pipe isconnected to a container containing a microbubble-containing solution,said stimulation is compression, expansion and swirling currentgenerated by circulating part of the microbubble-containing solution inthe container by the circulation pump and making the solution paththrough an orifice or porous plate having a single or multiple holesinstalled in the circulation pipe.
 11. The method according to claim 10,wherein the circulation pump gives a positive pressure of 0.1 MPa ormore to the discharge side.
 12. The method according to claim 10,wherein the circulation pump gives a negative pressure lower than theenvironmental pressure to the intake side.
 13. The method according toclaim 1, wherein, when a circulation pipe is connected to the containercontaining a microbubble-containing solution, the stimulation iscompression, expansion and swirling current generated by feeding themicrobubble-containing solution in the container into the circulationpipe and making the solution path through an orifice or porous platehaving a single or multiple holes installed in the circulation pipe. 14.The method according to claim 1, wherein the stimulation is forciblyinternal circulation, in the pipe for feeding the microbubble-containingsolution generated by a microbubble generator to a container, of makingthe microbubble-containing solution discharged from the microbubblegenerator pass through a punching plate installed in the pipe, taken inpart of the microbubble-containing solution from an intake installedbetween the punching plate and the container and feeding it into a pump,feeding the microbubble-containing solution into the pump, dischargingit form an outlet port installed between the microbubble generator andthe punching plate, and making it pass through the punching plate onceagain.
 15. The method according to claim 14, wherein, the pump gives apositive pressure of 0.1 MPa or more to the discharge side.
 16. Themethod according to claim 14, wherein the pump gives a negative pressurelower than the environmental pressure in the upstream pipe.
 17. Themethod according to claim 1, wherein, the stimulation is a catalyticreaction generated by allowing an oxidant to react in the presence of acatalyst.
 18. The method according to claim 17, wherein the catalyst iscopper and the oxidizer is ozone or hydrogen peroxide.